Past investigations have indicated that light-induced carotene synthesis in photochromogenic mycobacteria consists of photochemical reaction followed by a series of dark reactions which eventually lead to substantial carotene production. A number of parameters of both steps have been investigated to elucidate the biochemistry of this photoresponse. An interesting observation has also been made that antimycin A can substitute for the photochemical reaction, and that it does so by a mechanism other than through interference in the electron transport system. It is the objective of this proposal to continue these studies with the focus on the mode of action of light and antimycin A, and the preparation of a soluble enzyme system capable of synthesizing carotenes. The studies on the mode of action of light and antimycin A will be undertaken to provide further evidence that specific protein synthesis is, perhaps, induced by these agents. Development of a soluble enzyme system will permit a detailed understanding of the light-dependent carotenogenesis in mycobacteria. Studies will also be conducted to determine the effect of light and antimycin A on the enzymes involved in nucleic acid metabolism.